Electrical induction apparatus having graded insulation



Feb. 9, 1960 F. A. HATFIELD 9 2,924,799

ELECTRICAL INDUCTION APPARATUS HAVING GRADED INSULATION Filed June 21.1957 66 78 mvgmon. 2 FREDERICK A HATFIELD E?? 2%", L4; sh

ATTORNEYS United States Patent ELECTRICAL INDUCTION APPARATUS HAVINGGRADED INSULATION Frederick A. Hatfield, Zanesville, Ohio, assignor toMcGraw-Edison Company, Milwaukee, Wis., a corporation of DelawareApplication June 21, 1957, Serial No. 667,142

12 Claims. (Cl. 336-185) This invention relates to electrical inductionapparatus and particularly to high voltage coils or windings such asthe'primary winding in distribution- -transformers.

High voltage windingssuch as employed in distribution transformers arewound with a plurality of concentric layers of coil turns with thelayers separated by electrical interlayer insulation. The coil turns andthe coil layers may be series connected to add the voltage of theseparate turns.v 'In Winding the coil, the coil layers-are wound backand. forth from a continuous conductorsuch that the voltage between theend turns of successive layers is alternately equal to zero and to thesum of the voltages of the individual coil turns in two layers. As thelength of the coil increases, the voltage per coil layer also increasesand the insulation required between layers, particularly immediatelyadjacent-the end turns having the high'potential difference, increasesto such an extent that it is not always practical to provide adequateinsulation.

A practicalsolutionin high voltage coils is the use ofback-turn-sections wherein the winding-is axially divided into aplurality of individual coil sections which are connected inseries. Theadjacent coils are wound in opposite directions and alternatelyconnected at the inner and outer coil layers to maintain positivevoltage summation. The axial lengths of the coil sections are madesufficiently short to prevent a build up of large voltages per layer andthereby reduce the maximum voltage difierence between adjacent layers.Therefore, the winding can be formed without the use of unwieldlythickness of interlayer insulation. However, in this method,'potentialdifierences will exist between the adjacent coil sections not only dueto the summation of the voltages of the individual coil turns in theadjacent coil sections but also due to the distribution of irregularpeaked voltage waves or surgesto which the winding may be'subjectedbecause of lightning, switching, or the like. Normally, in the design ofthe coil sections, a maximum potential difference which is expected tooccur between coil sections is determined or calculated. Sufiicientintersection insulation having a constant axial thickness is providedbetween the coil sections to prevent flashover from one coil section,commonly by spacing the adjacent end coil turns in adjacent coil layersto provide the required insulating space and by crimping or folding theedge of the radially outermost piece of interlayer insulation uponitself to a thickness suflicient to mechanically lock the coil turnsagainst axial movement. The voltage between coil sections is differentat various radially spaced points corresponding generally to thediiferent adjacent layers of adjacent coil sections. Equal insulation isinserted for the radial depth of the coil sections and consequently anexcess intersection insulation exists at other than the position orpoints of maximum voltage diiierence.

In accordance with the present invention, the insulation disposedbetween adjacent coil sections is graded to more nearly conform to theactual voltage distribution therebetween. This provides a higher ratioof winding space to insulation space and thus permits not only economyof insulation and the like but also more eficient use of thespace withinthe core window. The intersection insulation is provided by radiallyfolded extensions of all or part of the interlayer insulation. Theintersection insulation is then simply and easily step-graded by eithervarying the width of the folds or by varying the number of folds orboth.

The accompanying drawing illustrates the best mode presentlycontemplated by the inventor for carrying out the invention.

In the drawing:

Figure 1 is a perspective view of a distribution transformer;

Fig. 2 is an enlarged fragmentary view representative of theconstruction of the primary winding in a distribution transformer, takenon a plane through the axis of the winding; and

Fig. 3 is a view similar to Fig. 2 of another embodiment of theinvention.

Referring to the drawing and particularly Fig. l, a laminated core 1 ofthe wound strip type has a secondary winding 2 wound on each leg and aprimary winding 3 superposed upon the secondary winding. Interwindinginsulation 4 normally including a plurality of superposed layers ofpaper, fabric or the like is disposed between the windings 2 and 3.

Transformers may be employed to deliver high voltage, low-current powerto a load as low-voltage, high-current power. The primary winding isthen the high voltage winding and is wound with a relatively largenumber of coilturns of small diameter wire which safely carries therelatively small current.

Referring to Fig. 2, a fragmentary portion of a transformer is shownwith, the secondary winding 2 partially shown, in outline only. Theprimary winding 3 is shown with cross sections of a relatively v fewcoil turns, substantially enlarged for purposes of illustration. Inactual construction, a much greater number of turns would be used.

The illustrated primary winding 3 comprises three individual coilsections, 5, 6 and 7 respectively. Each coil section is individuallywound from an uninterrupted conductor into three concentric layers 8, 9and 10 of a plurality of individual'coil turns.

Beginning with coil section 5, the first coil layer 8 is wound upon twotubular sheets of interlayer insulation 11 and 12 of paper or othersuitablefabric. The coil layer 8 is started with a first, turn 13, shownto the right of coil section .5 in Fig. 2,, and is wound from right toleft and is terminated in a final coil turn 14, shown to the. left insection 5 of Fig. 2. The coil turns in layer 8 of coil section 5 areassumed for purposes of illustration to be wound in a clockwisedirection looking to the right in Fig. 2. The last turn 14, of layer 8is integrally connected with a first coil turn 15 in the second coillayer 9. The coil turn 15 is wound directly over the turn 14 and thesecond layer 9 is wound upon two sheets of interlayer insulation paper16 and 17. The second layer 9 is wound from left to right in Fig. 2 backover-the first coil layer 8. The second layer 9 terminates in a coilturn 18 which is. axially aligned with the first turn 13 of the firstcoil layer 8.

The corresponding interlayer insulation paper 11, 12, 16 and 17 for thefirst two coil layers 8 and 9-extends beyond the first and last turnsand is similarly crimped or folded upon itself to provide axialintersection insulation adjacent the end coil turns. The right end ofthe interlayer insulation paper 11 and 16 for respective coil layers 8and 9 projects beyond the coil turns 13 and 18, as at 19. The right endof the interlayer insulation paper 12 and 17 for the respective coillayers 8 and 9 is folded upon itself as at 20 to a suflicient portion ofthe thickness of the coil layers 8 and 9 to mechanically lock the coilturns in an axial direction and to provide intersectional or axialinsulation for the coil section 5. The length of the extensions 19 andthe axial width of folds 20 are the same and are determined by theminimum potential difference which will arise between corresponding coillayers in adjacent coil sections. In coil section of Fig. 2 a singlewidth is provided to the right end of section 5 as this is a position ofminimum potential as will more fully appear hereinafter.

The left end of the interlayer insulation 12 and 17 is folded uponitself adjacent the respective coil turns 14 and 15, as at 21 with thesame axial width as folds 20 and mechanically locks the coil turns in anaxial direction. The left end of the insulationpaper 11 and 16 isextended beyond the folds 21 and is similarly folded as at 22 to providea smooth outer end to the coil section 5. The left hand folds 22 ofinsulation 11 and 16 are made the same radial depth as the adjacentfolds 21 by folding each sheet of insulation 11 and 16 upon itself anadditional time.

The third coil layer of coil section 5 is formed by a series of coilturns wound from right to left in Fig. 2 with the first turn 23connected directly to the last turn 18 of the second coil layer 9. Thethird layer 10 of coil section 5 is wound back over a portion of thesecond layer 9 and terminates in a coil turn 24 which is ex tendedoutwardly of the coil section 5 to provide a connecting lead for theprimary winding 3. Two sheets of interlayer insulation paper 25 and 26separate the coil layers 9 and 10. The third layer 10 is shifted axiallyto the left in the drawing and away from the adjacent coil section 6 adistance equal to the width of one of the end folds in the interlayerinsulation to provide increased axial spacing of the corresponding coillayers 10 in coil sections 5 and 6. The interlayer insulation paper 25is folded upon itself as at 27 and the folded end is disposed in radialalignment with the right hand folds in the first two layers 8 and 9. Theleft end of paper projects beyond the last coil turn 24 as at 28 andterminates in alignment with the outer surface of the folds 22 in coillayers 8 and 9. The radially outer insulation paper 26 is folded at theright hand end as at 29 and fills the. space between the first coil turn23 of coil layer 10'and' the" folded end 27 of paper 25 which space iscreated by the shifting of the third layer with respect to the first twocoil layers. The left hand end of the radially outer interlayerinsulation 26 is folded as at 30 to provide insulation in alignment withthe outer edge of the first two layers.

Coil section 6 of the primary winding 3 is wound in a reverse directionsuch that the first layer 8 of coil section 6 is a continuation of thefirst layer 8 of coil section 5. The first coil layer 8 of coil section6 is wound,

starting with a first coil turn 31, from left to right in Fig.

2 and in a counterclockwise direction looking to the right in Fig. 2.The first coil layer 8 is wound upon two superposed sheets of interlayerinsulation paper 32 and 33 and terminates in an end coil turn 34, shownto the right in Fig. 2. The end coil turn 34 is extended to the secondlayer 9 and the second coil layer 9 is wound upon two superposed sheetsof interlayer insulation paper 35 and 36.

The second coil layer starts with the coil turn 37 which is superposedupon the last coil turn 34 of coil layer 8 and is wound back over thefirst coil layer 8 with the final turn 38 disposed about the first turn31 of the first coil layer 8.

The ends of interlayer insulation paper 32, 33, 35 and 36 of the firsttwo coil layers 8 and 9 of coil section 6 are folded in the reversedirection of the corresponding insulation paper for coil section 5. .Theradially innermost interlayer insulation papers 32 and 35 project beyondthe first and last coil turns 31 and 38, respectively,

as at 39 into abutment with the similar projections 19 in coil section5. The right hand end of insulation 32 and 35 is folded as at 40 anddisposed in spaced relation to the coil turns 34 and 37 of therespective coil layers 8 and 9 a distance equal to the axial width of asingle fold. The radially outermost interlayer insulation paper 33 and36 is folded at both ends as at 41 and 42. The folds 42 fill the spacebetween the coil turns 34 and 37 and the folds 40 of interlayerinsulation paper 32 and 35. The left hand end folds 41 abut thecorresponding end folds 20 in coil section 5 and provide insulationbetween the corresponding layers 8 and 9 of coil sections 5 and 6.

The third layer 10 of coil section 6 is axially oifset away from thecoil section 5, to the right in the Fig. 2, a distance equal to thewidth of a fold in the interlayer insulation paper. The third layer 10begins with a coil turn 43 which is a continuation of the last turn 38of the second layer 9 and is wound back over the second layer 9 to afinal coil turn 44. Interlayer insulation paper 45 and 46 is disposedbetween layers 9 and 10. The radially innermost layer of insulation 45is folded at the left end as at 47 in spaced relation to the initialcoil turn 43. The opposite end of the insulation paper 45 projectsbeyond the final coil turn 44 as at 48. The radially outermostinterlayer insulation paper 46 is folded at both ends as at 49 and 50 tomechanically lock the coil turns, thereby providing intersectioninsulation to each side of the third coil layer 10.

Thus four separate folds of insulating paper are provided between thethird layers 10 in the adjacent winding sections 5 and 6 to providemaximum insulation therebetween. The adjacent first coil turns 13 and 31of sections 5 and 6 are joined by a lead 51 to serially connect thewinding sections 5 and 6. Therefore, the coil turns 13 and 31 are at thesame potential and no axial or intersectional insulation is needed.While no intersectional insulation would actually be required at thispoint between the same layers, it is commonly accepted practice toprovide the same amount as in succeeding layers. Because the windingsections 5 and 6 are relatively short, the voltage difference betweenthe adjacent final coil turns 18 and 38 is still relatively small andthe two abutting folds 20 and 41 provide adequate insulation.

The potential difference between the adjacent coil layers 10 of windingsections 5 and 6 is substantially greater than the first two layersbecause they lie at opposite ends of the winding sections which areserially connected and add their voltages.

Coil section 6 is wound in the same manner as coil section 5 except in areverse direction.

The third coil section 7 is Wound and arranged on core 1 exactly as iscoil section 5 and thus is arranged in an opposite axial direction withrespect to coil section 6. Coil section 7 starts at the right of thecoil section 7 in Fig. 2 with the coil turn 52 in the first coil layer8. The first and second layers 8 and 9 are each wound upon twointerlayers of insulation 53 and 54 respectively with single folds ofinsulation 55 formed by folding the extended interlayer insulation 54upon itself on the right end of coil section 7 and with double folds ofinsulation 56 and 57 formed by folding the extended interlayers 53 and54 upon themselves to the left. The first layer of coil turns 8 is woundfrom right to left and the second layer 9 is wound from left to right asviewed in Fig. 2. The third layer 10 is wound upon two concentricinterlayers of insulation 58 and 59 and is offset to the left in Fig. 2as is the third layer of section 5. A single fold of insulation 60 isformed by folding the left end of extended interlayer 59 upon itself anda double fold of insulation 61 and 62 respectively, is formed by foldingthe right end of extended layers 58 and 59 upon themselves.

The last turn 63 in the layer 10 in the coil section 7 is connected tothe last turn 44 of section 6 by a lead 64. As these coil turns areconne t d tog t r, they are at the same potential and a.minimuminsulation' is required therebetween. However, between the firsttwocoil layers Sand 9 of section 7 and the first two coil layers 8-and 9oflsectiono, there isa substantial potential difference due factthatthevoltageat any coilturn within middle section 6 with respect to a coilturn of section 7 is equal to-z the sum-of the individualncoil turns insection 7 plus the 'individual" coilturns in section- 6 which connectthe two turns under consideration. The voltages of the coil turns-addand thus thevoltage at thecoil turns in section Sis-relatively high withrespectto the initial coil turns in section 7.

Referringto Fig. 3, a second embodiment of the invention: is-illustrated which employs a single fold of varyingaxial width-toprovide the necessary-radially graded insulation between. adjacent "coilsections. Corresponding elements in-Fig. 1 and Fig. 2-are-givencorresponding numbersunlessotherwise specifically described.

As in Eig-Z, the last coilturn 65- of coil section 5 in Fig. 3 isextended to :provide connection to one side of a powersource-andlikewisethe first'coil turn 66 of section 7 is also extended to provideconnection to the corresponding primarywinding-3 on the other leg ofcore 1. The end turn 67 in coillayer of section 7 is connected tothe-end turn'68 insection-6 and the starting coil turn 69 of sectiond incoil layer Sisconnected to the starting eoibturn 70 of section '5 incoil layer 8.

-Seotions=5-and-7-are similarly wound in Fig. 3. Two sheetsor' tubes'ofinterlayer insulation 71 and 72 are disposed between theradiallysuccessive coil layers 8, 9 and 10*. The firStlayer71-isgenerally tubular in shape and terminates adjacent the axialend ofthe coilsections. The first-layer 71 maybe omitted from underneaththe first coil layer-80p maybe wound-as one piece for all sections 5, 6and asra-part of -theinterwinding insulation'of Figure 1. The secondinterlayer insulation 72 is also disposed-between each layer andiscrimped or folded at each end. The-left ;hand projection andthe righthand projectio'nof the insulation 72 forsections 5 and 7 in the firstand second coil layer 8 and 9-is similarly crimped, as at 73 and-74,respectively. The width of the folds 73 which lie to the left endofthecoilsections in Fig. 3 is generally equal to the width of twoindividual folds employed in the embodimentof Fig. 2. The width ofthefolds 74 which lie' to the right end of the coil sections 5 and 7 inFig. 3 -,isgenerally-equal to'the width of one individual fold-employedin the embodiment of=F-ig.-2. Thus, the folds 73 and-74 san 3-establishthe same proportionate insulationwalue as the correspon'dinginsulationfolds 20, 21=and 22tandainsulation folds-55, 56 and 57ofcorresponding-coil "sections S'a-nd 7 in :Fig. 2. In the-third layer-ofcoil -sections 5 and7- of Fig. 3, the left hand projection ot-insulation72-is--a-single1widthfold as-at 75 and the'right handprojection is adouble width fold as at 76. -=The"-width of the fold 75 and 76 is thesame as the width of "the 1 individual folds 27, -29 and 30 in Fig. 2and thereforemrovide corresponding insulation.

- w-Incoil sectionfi, two layersof interlayer insulation 77 and :78 areinterposed between the successive coil layers 8; 9, audit). The firstlayer 77 is tubular and extends past the 'endturnsfof each coil layer totheaxial end of the coil section. This-piecemay also be omitted fromunderneath the first coillayer-8 orniay'be wound as one-piece for allsections '5, "6'and 7 as a part of the interwinding insulation 4:0fFigure 1. The second layer 78 is also tubulanand extendstpast theendturns of'each coil layer with-the extended portionbeing folded uponitself to establish the intersectional electrical insulation. The lefthandfolds 79-for the layers 8 and 9 are the same width as theindividualfolds of "Fig. 2, and therefore provide minimu'rninsulation between coilsectionsS and 6 at the positionof minimumpotential difference. Theright'hand folds 80'ofinsulation in; layers-8 and 9 are double-widthfolds'a'nd' thereforerprovide maximum insulation between 'o'oilsectionsd and 7 at -.p0intsof greatest potential difference. Forthethird layer 10 of coil sections 6 of Fig, 3, the left hand vfold.81is a double width fold and the rightband fold 82 isa single width fold.Maximum insulation is thereforeprovided between coil sections 5 and 6 inthe third layer which is a position of maximum poten tial difference.Thus, inbothFig. 2. and Fig. 3, the same intersectional insulationdistribution is obtained. The distribution in both constructions beinggenerally in accordance with the actual potential existing between theexisting coil sections.

'In both illustratedembodiments, the insulation folds lie in a generallyaxial direction to establish insulation between coils sections inaccordance with the radially varying axial potential established betweenthe adjacent coil section. -If desired, the insulation folds may lie ina radial direction with the width of the individual folds filling theradial space between successive layers and the number of folds varyinginaccordance with the desired insulating distribution.

The illustrated embodimentsof the invention shows thesame odd-number ofcoil layers in each coil section and an equal-number of turns in eachlayer such that the connected turns'of adjacent coils are immediatelyadjacenteach other. In general practice this is seldom attained duetovariations in the winding apparatus and the wire'employed,particularly where many turns of fine wire are used. Thus, although, thelast turn of each section falls in the final layer, it often emergesfrom the center or oppositeend of the coil section and is extendedaxiallytothe other coil section. Nevertheless, forpraetical,purposes,;the voltage between adjacent turns of the-finallayersdoes notappreciably vary regardless ofwhere thefinal turn emerges.The designernormally assumesJfull maximum voltage: occurs between theadjacent final or-outer layers for .purposes of design.

Although the illustrated winding employs three individual' coil sectionseach having only three individual layers of coil'turns, any othersuitable number of coil sections and/or coil layers may beemployed. Theillustrated intersectional insulation is shown step-graded because itis, a simple and practical form of construction. If desired, a smoothlyprogressively changing intersectional insulation may be employed.

:In-makin'g the axial shift in the coil layers to change the insulatingspacing of adjacentcoil sections, a transitionallayer may advisably' beemployed. The transitional layer would be axially shortened to disposeits initial turn in alignment with the preceding final turn and itsfinal turn in'axialalignment with the initial turn of the nextsucceeding layer. The transitional layer would provide a smooth shift atthe change of insulation and would-eliminate sharp bends-and spacebetween the coil turns.

The present invention provides a high voltage winding having in higherratio of winding; space to'insulation space and permitting-greatereconomy of insulating material and other cooperatingcomponents-such asthe core and. housing. Further, varying the width or number of end foldsof the interlayerinsulation provides a simple constructionfor a radiallystep-graded insulation of adjacent'coil sections.

Various modes of carrying out the invention are contemplated as beingwithin the scope of the following claimszparticularly pointing out anddistinctly claiming the subject matter which is regarded as theinvention.

I claim:

1. In induction apparatus, a plurality of multilayer coil. sectionsaxially mounted in side by side relation and interconnected in anelectrical circuit with a radially varying potential established betweenadjacent coil'sections under operating conditions, and at least onelayer of insulation between corresponding superimposed layers of thecoil sections, certain of said insulation layers being individuallyreverse folded upon themselves immediately adjacent the ends. of thecoil layers to provide radially-graded insulation material disposedbetween said sections generally in accordance with the radially varyingaxial potential difference established under operating conditions toprevent fiashover between adjacent coil sections.

2. Electrical induction apparatus having a plurality of multilayer coilsections axially mounted in side by side relation and connected in aseries circuit, which comprises interlayer insulation disposed betweensuccessive winding layers of said coils and axially extended beyond theend turns of the coils, the extended portion of the insulation beingprefolded upon itself axially of the adjacent winding layer to provideelectrical insulation between adjacent coil sections, and the totalaxial width of said folded insulation between each pair of coils varyingin accordance with the potential between adjacent coil sections toprovide a radially-graded insulation be tween adjacent coil sections andthereby increase the ratio of available winding space to insulationspace.

3. Electrical induction apparatus, which comprises a magnetic corestructure, a plurality of coil sections having an equal number of layersof continuous coil turns, said coil sections being axially aligned inside by side relation on said core structure and alternately having theinitial turns and the final turns of adjacent coil sections connectedtogether, alternate coil sections being reverse wound to establish apositive voltage summation of said coil sections, each coil sectionhaving certain of said layers axially offset to establish a spacingbetween layers of adjacent coil sections in proportion to the potentialdifference arising between aligned layers of adjacent coil sections, andelectrical insulation disposed within the space between said adjacentcoil sections to prevent flashover between adjacent coil sections saidinsulation characterized by being formed in layers disposed between thelayers of the coil sections and having their ends folded radially andaxially in a plurality of reverse bends adjacent the ends of thecorresponding coil section layers and in alignment therewith.

4. A high voltage winding wound on a magnetic core structure, whichcomprises a plurality of coil sections each having a plurality of layersof continuous coil turns, the axial length of each of said layers beingsubstantially the same, electrical insulating fabric disposed betweensuccessive layers and extended axially therefrom with the ends of saidfabric being folded radially and axially in reverse bends to provideoppositely steppedgraded axial insulation on opposite ends of said coil,said coil layers being axially ofiset to maintain said coil section of aconstant axial length, and a core structure having said coils arrangedin axial alignment on the core structure with alternate coils axiallyreversed to dispose corresponding widths of axial insulation in abuttingrelation.

5. A high voltage winding, which comprises a core structure, a pluralityof coil sections arranged in axial alignment on said core structure andeach having a plurality of layers of series-connected coil turnsbeginning at the innermost layer and terminating in the outermost layer,alternate coil sections having the initial coil turns at correspondingaxial ends and being reverse wound with respect to the adjacent coilsections to alternately dispose the initial turns adjacent each other,the axial length of each layer in said coil sections being substantiallythe same as all other layers, electrical insulation interposed betweenthe layers and extended axially of the layers, the ends of saidinsulation being radially and axially folded in reverse bends adjacentand aligned with the corresponding coil section layers to axially lockthe coil turns in the adjacent outer coil layer and to provide axialinsulation, the axial width of folded insula' tion varying at oppositeends of each coil section in predetermined steps alternately from aminimum to a maximum and from a maximum to a minimum between theinnermost layer and the outermost layer in accordance with the changingpotential existing between adjacent coil sections, and said coil layersbeing axially offset in accordance with said varying insulation width tomaintain a constant axial coil section length and to disposecorresponding widths of axial insulation in abutting relation. I

6. Induction apparatus having a plurality of multilayer coil sectionsconnected in series and disposed'in side by side relation on a core andhaving certain coil sections reverse wound to provide an increasingvoltage summation, which comprises at least one interlayer of insulationbetween successive winding layers of each coil section, and at least oneof said interlayers of insulation being extended axially of theassociated coil section and being folded radially and axially' uponitself to establish at least one axially extended folded portion toprovide electrical insulation between aligned coil layers of adja-' centcoil sections, the number of said extended folded portions varying andestablishing axial insulation generally in accordance with the potentialdifference between the coil layer of the immediate coil section and analigned coil layer of the adjacent coil section.

7. In a high voltage winding having a plurality of serially-connectedmultilayer coil sections disposed in side by side relation with thesections reverse wound with respect to the adjacent coil sections toalternately dispose initial turns, said coil sections having adjacentinitial turns connected and final turns connected to pro vide increasingvoltage summation and each coil section comprising a plurality ofconcentric layers'of coil turns wound from a continuous conductor, aplurality of intervening layers of insulation interposed between andaxially extended from said concentric layers of coil turns, one or morefolded extensions of said insulation formed by radial and axial foldsproviding reverse bends disposed adjacent and in alignment with theaxial ends of the corresponding coil turns, and the number of saidfolded extensions adjacent the ends of radially successive layersincreasing from a minimum to a maximum in general proportion to thepotential difference between the immediate layer of coil turns and thecorresponding layer of coil turns of the immediately adjacent coilsection.

8. A high voltage winding, which comprises a magnetic core structure,two or more multilayer coil sections disposed in side by side relationupon said core structure, said coil sections being alternately reversewound from an inner start layer to a final layer, means to connect saidcoil sections in series by alternate connection of the inner layer endsand outer layer ends of adjacent coil sections to provide a positivevoltage summation, two or more concentric layers of insulationinterposed between layers of coil turns in each coil section, the endsof each of said intervening layers with a layer of coil turns woundthereon being radially folded immediately adjacent the axial end turnsfor the depth of the winding layer wound thereon to mechanically supportthe winding layer in an axial direction and to establish insulationbetween adjacent coil sections, the ends of certain other layers of saidintervening layers extending beneath said folds and being radiallyfolded immediately adjacent the first folds for the depth of the windinglayer wound thereon and disposed in axially abutting relation with thefirst folds to increase the insulation between certain aligned layers ofadjacent coil sections, and the corresponding coil layers wound on saidlast named intervening layers being axially offset to maintain aconstant axial dimensioned coil section.

9. A coil section for a high voltage winding having a plurality of sideby side and alternately reverse-wound coil sections connected in seriesby connection between end turns of'adjacent coil sections, whichcomprises a plurality of concentrielayers of continuous coil turns ineach coil section, said concentric layers being dis- P ed in g eralradial alignment and having relatively high potential diflierencebetween certain of said aligned layers, and said layers having thehigher potential difference being axially offset with respect to otherof said concentric layers, two or more tubular interlayer insulatorsdisposed between concentric layers to prevent elec trical flashoverbetween layers, the ends of the insulators being extended past the endsof the coil turns and each being radially outwardly folded upon itselfto provide insulation adjacent the axial ends of the coil, the insulatorupon which the corresponding layer of coil turns is immediately woundbeing folded adjacent the end coil turns in the layer, and the otherinsulators being folded in axially outwardly abutting relation to saidfirst insulator and to each other to dispose the axial end of the coilsection in a radial plane whereby greater axial insulation is providedbetween coils turns having an increased potential difference.

10. A high voltage winding, which comprises a plurality of individualmultilayer coil sections disposed in axially abutting relation and eachhaving a number of coil turn layers with a radially inner terminal atone axial end of the coil and a radially outer-terminal gen erally atthe opposite axial end of the coil, means to join said adjacent coilterminals to connect the coil sections in series, the adjacent coilsbeing wound in a reverse direction to dispose common potential terminalsin generally side by side relation and to establish positive voltagesummation of the individual coil sections, adjacent ends of the coilsections having a radially varying potential gradient therebetween whichis the inverse of the potential gradient of the immediately adjacentcoil sections, interlayer insulation disposed between the coil layers ofeach coil section and crimped at each end into a radially extended foldhaving an axial reverse bend immediately adjacent the end of theassociated coil layer, the axial width of the successive folds beingvaried in predetermined steps in general accordance with the potentialdifference established between the aligned coil layers of adjacent coilsections, and the coil layers being axially shifted to permit radiallyinverse disposition of the insulation at the opposite axial ends of eachcoil. j

ll. A high voltage winding, which comprises a core structure, aplurality of similar coil sections each having a plurality of concentriclayers having the same axial length and formed of continuous coil turnswound back and forth over the immediately preceding layer, said coilsections being arranged on said core structure in axial alignment andbeing alternately axially reversed to dispose initial starting coilturns adjacent each other, means to connect said adjacent initial coilturns and alternate final turns to serially connect said coil sections,a tubular electrical insulation of at least one layer of flexiblematerial interposed between successive layers and axially extended pastthe axial end turns, the extended end of at least one layer of saidinsulation being folded radially and axially to provide a plurality ofreverse bends and thereby build up axial insulation immediately adjacentthe axial end turns and varying in axial length between different layersin accordance with the potential established between the coil sections,and said coil layers being axially ottset to accommodate said varyingwidths with a constant axial coil section length.

12. Induction apparatus having a plurality of multilayer coil sectionsconnected together and disposed in side by side relation on a core andhaving certain coil sections reverse wound to provide an increasingvoltage summation, which comprises interlayer insulation disposedbetween successive layers of each coil section, said insulation beingextended axially of the associated coil section and being folded inreverse bends upon itself to establish axially extended folded portionsto provide electrical insulation between aligned coil layers of adjacentcoil sections, and the number of said extended folded portio'ns and theaxial extent of said folded portions varying to establish axialinsulation generally in accordance with the potential difference betweenthe coil layer of the immediate coil section and the aligned coil layerof the adjacent coil section.

Gilinson Apr. 3, 1923 Carnilli Oct. 3, 1944

